156 Royal Society : — 



la obtaining the above averages, I was obliged to interpolate for 

 such changes as took place on Sundays or holidays, when no obser- 

 vations were taken. The interpolation, however, does not change the 

 general result, and on some accounts the Table is more satisfactory 

 than if the observations had been made with special reference to the 

 determination of the lunar influences, accompanied, as such a refer- 

 ence would very likely have been, by a bias to some particular theory. 



The thermometric and barometric averages show a general corre- 

 spondence in the times of the monthly maxima and minima, — the 

 correspondence being most marked and uniform at midnight, when 

 the air is most removed from the direct heat of the sun, and we 

 might therefore reasonably expect to find the strongest evidences of 

 the relations of temperature to lunar attraction. 



By taking the difference between the successive weekly tides, we 

 readily obtain the amount of barometric effect in each quarter. The 

 average effect is more than three times as great in the third and fourth 

 quarters as in the remaining half-month, — a fact which suggests inte- 

 resting inquiries as to the amount of influence attributable to varying 

 centrifugal force, solar conjunction or opposition, temperature, &c. 



Although, as in the ocean tides, there are two simultaneous cor- 

 responding waves on opposite sides of the earth, those waves are not of 

 equal magnitude, the barometer being uniformly higher when the 

 moon is on the inferior meridian, and its attraction is therefore 

 exerted in the same direction as the earth's, than when it is on the 

 superior meridian, and the two attractions are mutually opposed. 

 Some of the views of those who are not fully satisfied with the prevail- 

 ing theory of the ocean-tides, derive a partial confirmation fromthis fact. 



I find, therefore, marked evidences of the same lunar action on 

 the atmosphere as on the ocean, the combination of its attraction 

 with that of the sun producing both in the air and water, spring 

 tides at the syzygies, and neap tides at the quadratures ; and I believe 

 that the most important normal atmospheric changes may be explained 

 by the following theory : — 



The attraction- and rotation-waves, as will be readily seen, have 

 generally opposite values, 4he luni-solar wave being 



Descending, from 0° to 90°* and from 180° to 270°, 

 Ascending, from 90° to 180° and from 270° to 0° ; 

 while the rotation- wave is 



Ascending, from 330° to 60° and from 150° to 240°, 

 Descending, from 60° to 150° and from 240° to 330°. 



From 60° to 90° and from 240° to 270°, both waves are descend- 

 ing, while from 150° to 180° and from 330° to 360° both are 

 ascending. In consequence of this change of values, besides the 

 principal maxima and minima at the syzygies and quadratures, there 

 should be secondary maxima and minima f at about 60° in advance 

 of those points. 



* Counting 9 from either syzygy. 



f The secondary maxima and minima should correspond with the daily max- 

 ima and minima, which occur at St. Helena at about 4 h and 10 h a.m. and p.m., 

 giving = 60° a maximum, and = 150° a minimum. 



